The present invention relates generally to beamformers for arrays of receiving or transmitting elements. More specifically, but without limitation thereto, the present invention relates to ground-based digital beamforming for stratospheric communications platforms.
In ground-based digital beam forming, the individual element signals of an antenna array on a stratospheric platform are linked with a ground station so that the beamforming calculations may be performed by hardware that is not subject to the power, size, and weight constraints of the stratospheric platform. In conventional digital beamforming methods, each element signal is multiplied by a different phasor corresponding to a selected beam, for example ejxcex8i, where xcex8i is a phase angle calculated for each element i. The phasor products are then summed to form the selected beam. The phasors are selected so that signals arriving from a preferred direction add substantially coherently, while signals arriving from other directions add incoherently. The result is a spatial discrimination favoring signals arriving from the preferred direction and a corresponding enhancement of their signal-to-noise ratio. A problem with conventional digital beamformers is the requirement of a phasor multiplication for each element signal, typically N2 for an Nxc3x97N array. A reduction in the number of multiplications required would save processing time and resources that could be dedicated to other tasks.
The present invention advantageously addresses the needs above as well as other needs by providing a method and apparatus for beamforming signals for an array of receiving or transmitting elements.
In one embodiment, the present invention may characterized as a method for beamforming that includes the steps of selecting a beam elevation and azimuth and grouping elements of an antenna array into element ensembles that are substantially aligned with a wavefront projection on the antenna array corresponding to the selected beam elevation and azimuth.
In another embodiment, the present invention may characterized as a beamformer that includes a beam selector for selecting a desired beam elevation and azimuth and an ensemble selector for grouping elements of an antenna array into element ensembles that are substantially aligned with a wavefront projection on the antenna array corresponding to the selected beam elevation and azimuth.
The features and advantages summarized above in addition to other aspects of the present invention will become more apparent from the description, presented in conjunction with the following drawings.